This invention relates to electrical feedthroughs of improved design and to their method of fabrication. More particularly, the present invention relates to a process for depositing a protective metal coating over components of feedthroughs which are susceptible to oxidation.
Electrical feedthroughs serve the purpose of providing an electrical circuit path extending from the interior of a hermetically sealed container to an external point outside the container. For example, in implantable medical devices, such as implantable pulse generators (IPG's) including heart pacemakers or defibrillators and the like, the feedthrough assembly comprises one or more conductive terminal pins supported by a hermetic insulator structure for conductive feedthrough passage from the exterior to the interior of the medical device. Many such feedthroughs are known in the art which provide the electrical path and seal the electrical container from its ambient environment. Such feedthrough assemblies typically include a ferrule, the terminal conductor pin(s) or lead(s), and a hermetic glass or ceramic seal which supports the pin within the ferrule. It has recently been discovered that such electrical devices can, under some circumstances, be susceptible to electromagnetic interference (EMI). For example, EMI can inhibit pacing in an IPG. Devices have been developed, including the device of U.S. Pat. No. 5,333,095 to Stevenson et al. (the contents of which are hereby incorporated by reference), which have addressed this problem by incorporating a coaxial capacitor structure within the feedthrough assembly to shunt any undesirable EMI at the entrance of the IPG at high frequencies.
One of the more popular (and least expensive) materials for use as a medical implant terminal pin is tantalum, as it is one of a relatively few pin materials which is both highly conductive and biocompatible (other such pin materials include niobium and platinum). Unfortunately, tantalum is susceptible to oxide growth which can, depending on its extent, act as an insulator instead of a conductor over the surface of the pin. During fabrication of a feedthrough/capacitor combination, the tantalum pin is subjected to one or more heat treatments which can encourage oxidation, affecting the conductivity of the tantalum pin and its ability to make good electrical connections between other elements including the coaxial feedthrough capacitor and so forth.
Attempts have been made to coat the terminal pins with a conductive protective coating to prevent or discourage oxidation. One such method is described in U.S. Pat. No. 5,406,444 to Seifried et al. (the contents of which are hereby incorporated by reference). The Seifried '444 patent discloses a method of coating the terminal pins by vacuum depositing a metal coat by sputtered coating. This is preferably done before the terminal pins are encased in the glass insulator as a more elaborate sputtering fixturing technique is required after the terminal pins are sealed in glass.
There remains, however, a need for a process for applying a protective coating on terminal pins and other conductive components of assembled feedthrough assemblies, which does not require vacuum depositing nor elaborate sputtering techniques. The present invention fulfills this need and provides other related advantages.